s practice
   is not universal, and calendar differences can cause confusing
   differences between what Python and Matplotlib give as the number of days
   since 0001-01-01 and what other software and databases yield.  For
   example, the US Naval Observatory uses a calendar that switches
   from Julian to Gregorian in October, 1582.  Hence, using their
   calculator, the number of days between 0001-01-01 and 2006-04-01 is
   732403, whereas using the Gregorian calendar via the datetime
   module we find::

     In [1]: date(2006, 4, 1).toordinal() - date(1, 1, 1).toordinal()
     Out[1]: 732401

All the Matplotlib date converters, tickers and formatters are timezone aware.
If no explicit timezone is provided, :rc:`timezone` is assumed, provided as a
string.  If you want to use a different timezone, pass the *tz* keyword
argument of `num2date` to any date tickers or locators you create.  This can
be either a `datetime.tzinfo` instance or a string with the timezone name that
can be parsed by `~dateutil.tz.gettz`.

A wide range of specific and general purpose date tick locators and
formatters are provided in this module.  See
:mod:`matplotlib.ticker` for general information on tick locators
and formatters.  These are described below.

The dateutil_ module provides additional code to handle date ticking, making it
easy to place ticks on any kinds of dates.  See examples below.

.. _dateutil: https://dateutil.readthedocs.io

Date tickers
------------

Most of the date tickers can locate single or multiple values.  For example::

    # import constants for the days of the week
    from matplotlib.dates import MO, TU, WE, TH, FR, SA, SU

    # tick on Mondays every week
    loc = WeekdayLocator(byweekday=MO, tz=tz)

    # tick on Mondays and Saturdays
    loc = WeekdayLocator(byweekday=(MO, SA))

In addition, most of the constructors take an interval argument::

    # tick on Mondays every second week
    loc = WeekdayLocator(byweekday=MO, interval=2)

The rrule locator allows completely general date ticking::

    # tick every 5th easter
    rule = rrulewrapper(YEARLY, byeaster=1, interval=5)
    loc = RRuleLocator(rule)

The available date tickers are:

* `MicrosecondLocator`: Locate microseconds.

* `SecondLocator`: Locate seconds.

* `MinuteLocator`: Locate minutes.

* `HourLocator`: Locate hours.

* `DayLocator`: Locate specified days of the month.

* `WeekdayLocator`: Locate days of the week, e.g., MO, TU.

* `MonthLocator`: Locate months, e.g., 7 for July.

* `YearLocator`: Locate years that are multiples of base.

* `RRuleLocator`: Locate using a `rrulewrapper`.
  `rrulewrapper` is a simple wrapper around dateutil_'s `dateutil.rrule`
  which allow almost arbitrary date tick specifications.
  See :doc:`rrule example </gallery/ticks/date_demo_rrule>`.

* `AutoDateLocator`: On autoscale, this class picks the best `DateLocator`
  (e.g., `RRuleLocator`) to set the view limits and the tick locations.  If
  called with ``interval_multiples=True`` it will make ticks line up with
  sensible multiples of the tick intervals.  For example, if the interval is
  4 hours, it will pick hours 0, 4, 8, etc. as ticks.  This behaviour is not
  guaranteed by default.

Date formatters
---------------

The available date formatters are:

* `AutoDateFormatter`: attempts to figure out the best format to use.  This is
  most useful when used with the `AutoDateLocator`.

* `ConciseDateFormatter`: also attempts to figure out the best format to use,
  and to make the format as compact as possible while still having complete
  date information.  This is most useful when used with the `AutoDateLocator`.

* `DateFormatter`: use `~datetime.datetime.strftime` format strings.
é